Fabrication Of Oxide Thin-film Transistors Research Articles

Solution-Processed Metal Oxide Thin-Film Transistor at Low Temperature via A Combination Strategy of H2 O2 -Inducement Technique and Infrared Irradiation Annealing.

Solution processing has emerged as a promising technique for the fabrication of oxide thin-film transistors (TFTs), offering advantages such as low cost, high throughput, and exceptional compositional control. However, achieving reasonable electrical properties typically demands high annealing temperatures in the fabrication process. In addressing this challenge, a novel combination strategy is proposed that involves integrating the H2 O2 inducement technique with infrared (IR) irradiation annealing. The study investigates the effects of precursors and IR irradiation annealing temperatures on the electrical properties of In2 O3 TFTs. It is found that H2 O2 can help accelerate the decomposition of organic residues, while IR irradiation annealing could enhance the film densification. By employing the proposed strategy, metal oxide TFTs consisting of a Zr-Al-O dielectric fabricated at 230°C and an In2 O3 channel layer fabricated at 185°C demonstrated high performance with field-effect mobility = 31.7 cm2 V-1 ·s-1 , threshold voltage = 1.3 V, subthreshold swing = 0.13 V per decade, and on-to-off current ratio = 1.1 × 105 . This work demonstrates the proposed combinational strategy is a general method to fabricate not only metal oxide semiconductorsbut also dielectrics.

Improving the Electrical Properties of Zinc-Tin Oxide Thin-Film Transistors by Additive using Electrohydrodynamic Jet Technology

Oxide thin-film transistors (TFTs) are important semiconductor materials for display backplanes. To fabricate flexible displays, not only display modes but also TFTs are important. Flexible TFTs are especially needed for flexible displays, and related processes need to be developed. Printing is a good choice for the new fabrication of oxide TFTs. Electrohydrodynamic (EHD) jet printing is an excellent alternative for making flexible TFTs. To improve the electrical properties of oxide TFTs using EHD jet printing, propylene monomethyl ether acetate (PGMEA) was added to a zinc-tin oxide (ZTO) formulation. EHD jet printing was performed by Taylor cone jet mode with parameters of 2.4 kV and 0.064 µL/s to obtain uniform thin films at a substrate temperature of 50oC. Much improved TFT properties were obtained, including a mobility of 7.11 cm2/V s, on-to-off current ratio of 2.8 × 106 and subthreshold slope of 1.44 V/dec for ZTO TFT with 5 wt% of PGMEA, and a mobility of 1.43 cm2/V s, on-to-off current ratio of 2.7 × 105 and subthreshold slope of 1.32 V/dec for the ZTO TFT. Almost no hysteresis behavior was observed in the oxide TFTs with added PGMEA. We report a new way to improve the electrical properties of oxide TFTs, by the simple addition of PGMEA.

(Invited) Fabrication Technique for Low-Temperature Aqueous Solution-Processed Oxide Thin-Film Transistors

Solution-processing of oxide semiconductor is a promising technique for the simple and low-cost fabrication of oxide thin-film transistors (TFTs). We demonstrate improved TFT characteristics by application of a hydrogen injection and oxidation (HIO) process to the fabrication of high-performance low-temperature oxide TFTs. The compatibility of this technique for flexible substrates was also confirmed when the HIO method was applied to solution-processed metal oxide TFTs.

(Invited) Low-Temperature Activation Method for InGaZnOx Thin-Film Transistors

Metal oxide thin-film transistors (TFTs) have attracted considerable attention for use in next-generation high-definition and large-area flat-panel displays (FPDs) owing to their excellent electrical properties such as high mobility (>10 cm2/Vs), large-area uniformity, and compatibility with low-temperature process. An InGaZnOx (IGZO) is widely employed as a channel material of oxide TFT. Although an IGZO film can be deposited by sputtering without an intentional substrate heating, an IGZO TFT requires a post-annealing around 300°C due to the recovery defective states induced during the sputtering process. A post-annealing required for improving TFT characteristics and reliability is often named as “activation annealing”. The activation annealing around 300°C limits the fabrication of oxide TFTs on flexible substrates. Several activation methods for oxide semiconductor, such as simultaneous UV and thermal annealing, electrical assisted thermal annealing, and high-pressure annealing, have been proposed to reduce annealing temperature at ~150°C. Another approach is an improving film quality of the sputtered IGZO. In this presentation, a new method to achieve high quality sputtered IGZO film will be presented. Proposed deposition method reduced density of states near conduction band, and could reduce an activation annealing temperature to 150°C. Detail mechanism to achieve low-temperature activation of IGZO TFT will be discussed.

Non-ideal current drop behavior in ultra-thin inorganic a-InGaZnO thin film transistors

Recent research in flexible and imperceptible electronic devices has been dominated by the development of robust channel materials and adequate processes for thin-film transistors (TFTs) based on an inorganic amorphous oxide. Water-soluble sacrificial polyvinyl alcohol and parylene were employed for the fabrication of ultra-light amorphous In–Ga–Zn–O (a-IGZO) TFTs with a top-gate configuration. But, a higher negative gate bias stress (≥5 V) caused anomalous degradation in the on-current level and field-effect mobility with increasing stress time, which was attributed to the rough surface of the chemical vapor deposited parylene film. The current work adopts an ultraviolet ozone irradiation treatment for improving the surface roughness of the polymer films prior to the fabrication of oxide TFTs. A suppression of the on-current drop and typical TFTs transfer behavior were observed under light irradiation with a negative gate bias stress. The a-IGZO TFTs on the parylene surface treated for 20 min exhibited a device thickness of approximately 5 µm and good TFT performances with field-effect mobility, subthreshold swing, and on/off current ratio values of 13.9 cm2/V s, 0.24 V/dec, and 7 × 108, respectively. This survey suggests that a polymer film with a smooth surface can play a beneficial role in fabricating flexible ultra-slim a-IGZO TFTs.

Application of hydrogen injection and oxidation to low temperature solution-processed oxide semiconductors

Solution-processed oxide semiconductors are promising candidates for the low cost, large scale fabrication of oxide thin-film transistors (TFTs). In this work, a method using hydrogen injection and oxidation (HIO) that allows the low temperature solution processing of oxide semiconductors was demonstrated. We found that this method significantly decreases the concentration of residual species while improving the film densification. Additionally, enhanced TFT performance was confirmed following the use of processing temperatures as low as 300 °C. The proposed process is potentially applicable to the fabrication of a wide variety of solution-processed oxide semiconductors.

An ‘aqueous route’ for the fabrication of low-temperature-processable oxide flexible transparent thin-film transistors on plastic substrates

Metal-oxide semiconductors have attracted considerable attention as next-generation circuitry for displays and energy devices because of their unique transparency and high performance. We propose a simple, novel and inexpensive ‘aqueous route’ for the fabrication of oxide thin-film transistors (TFTs) at low annealing temperatures (that is, <200 °C). These results provide substantial progress toward solution-processed metal-oxide TFTs through naturally formed, unique indium complex and post annealing. The fabricated TFTs exhibited acceptable electrical performance with good large-area uniformity at low temperatures. Additional vacuum annealing facilitated the condensation reaction by effectively removing byproduct water molecules and resulted in the activation of the In2O3 TFT at low annealing temperatures, even temperatures as low as 100 °C. In addition, we have demonstrated that the flexible and transparent oxide TFTs on plastic substrates exhibit good resistance to external gate bias stress.

Simple Aqueous Solution Route for Fabrication High Performance Oxide TFT

Metal oxide semiconductor attracts considerable attentions for driving circuit of next generation displays and energy devices owing to their simultaneous transparency and high electrical performance. We report fluorine doped zinc tin oxide (ZTO:F) and indium zinc oxide (IZO) thin-film transistors (TFT) via aqueous route. The aqueous route enables the fabrication of oxide TFT at low temperature with reasonable cost. The ZTO:F TFT exhibits good electrical performance and stability over electrical stress due to the effective removal of oxygen vacancy and generation of carrier by F doping. The IZO TFTs also shows good performance in terms of mobility and operation accuracy. Finally, the optimized IZO TFT is fabricated on plastic substrate with 250 ℃ annealing and the device exhibits sufficient performance for operation of various displays and basic circuitries.

Thermal analysis of amorphous oxide thin-film transistor degraded by combination of joule heating and hot carrier effect

Stability is the most crucial issue in the fabrication of oxide thin-film transistors (TFTs) for next-generation displays. We have investigated the thermal distribution of an InSnZnO TFT under various gate and drain voltages by using an infrared imaging system. An asymmetrical thermal distribution was observed at a local drain region in a TFT depending on bias stress. These phenomena were decelerated or accelerated with stress time. We discussed the degradation mechanism by analyzing the electrical properties and thermal distribution. We concluded that the degradation phenomena are caused by a combination of Joule heating and the hot carrier effect.

Fabrication of Oxide TFTs with Al[sub 2]O[sub 3]/ZnO Gate Stacks Patterned Using a Dry Etching Method

In this paper, we describe a newly developed dry etching process for the fabrication of ZnO-based oxide thin-film transistors (TFTs). The dry etching behavior of ZnO and Al 2 O 3 thin films was systematically investigated by varying the etching gas mixtures and their mixing ratios in a dry etching system using high-density helicon plasma. We fabricated an oxide TFT using an Al 2 O 3 /ZnO gate stack patterned by dry etching and confirmed good device characteristics, in which the field effect mobility and the ratio of on/off drain currents were about 0.8 cm 2 /(V s) and 10 7 , respectively.